1. Field of the Invention
The present invention is directed to a method and apparatus for applying a coating to an eyeglass lens or mold. In particular, the method and apparatus of the invention may be adapted to apply a ultraviolet light curable scratch resistant coating to an eyeglass lens or mold.
2. Brief Description of the Prior Art
The application of a scratch resistant coating onto the surface of an optical element has been known for some time. A wide variety of techniques and materials for applying the abrasion resistant coating have been developed over the years. Common coating techniques involve applying a composition (e.g., "a monomer solution") onto the surface of an optical element by spin, dip, spray or flow coating.
Recently, developments in this field have involved in-mold coating techniques, in which a liquid coating is applied to a surface of a mold and then transferred to the lens as the lens and mold having the coating thereon are being cured.
U.S. Pat. No. 4,895,102 issued to Kachel et al. discloses a spin coater having a drawer mounted within a housing, slidable between front and rear chambers thereof. The rear chamber is where the coated lens is exposed to a mercury vapor actinic light.
In U.S. Pat. No. 4,447,468 issued May 8, 1984 to J. B. Keable, spindled photographic film discs are coated with an ultraviolet light curable protective coating apparatus which receives a developer spindle carrying a plurality of film discs at a receiving station.
U.S. Pat. No. 5,164,228 issued Nov. 17, 1992 to Peralta et al. reports a spin coating process which coats plastic ophthalmic lenses with a scratch-resistant coating.
Generally, spin coater apparatus utilize either heat, mercury vapor lamps, or ultraviolet light emitting lamps having electrodes as curing light sources. These lamps have relatively short lifetimes, partly because of their need to be constantly run, and partly because of their considerable warm-up period. Therefore, there is a need to develop a spin coater having a light emitting source that uses less power, has a longer life, and provides more efficient control over the degree of polymerization.
A disadvantage of prior art spin coaters is the tendency of excess monomer solution to contact other components of a coating application chamber or the wrong surface of the lens or mold. For instance, if the convex side of a lens or mold was being coated, sometimes the monomer solution would leak or be spilled to the concave side of the lens or mold. In such a case, the monomer solution on the concave side of the lens or mold would tend to cure with the other monomer solution, and thus leave a portion of the concave surface with a hardened burr or mark on it. This burr or mark was unsightly and often a problem since it was not as tintable as the areas on the concave surface that had not been accidentally coated with monomer solution.
Another disadvantage of some prior art apparatus for lens or mold coating is that environmental dust or hardened airborne monomer particles tended to contaminate the coatings, lenses, or molds, thus causing imperfections in the surfaces of the resulting coated lenses or molds.